PPP and L2TP: Remote Access Communications

PPP and L2TP: Remote Access Communications

by Uyless D. Black, Uyless Black

Hardcover

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Product Details

ISBN-13: 9780130224620
Publisher: Pearson Education
Publication date: 11/16/1999
Series: Prentice Hall Series in Advanced Communications Technologies
Pages: 219
Product dimensions: 7.31(w) x 9.58(h) x 0.84(d)

About the Author


Uyless Black is a widely known and respected consultant and lecturer on computer networks and data communications. He is the author of all the books in his Prentice Hall Series in Advanced Communications Technologies, including Voice Over IP, Residential Broadband Networking, ATM: Foundation for Broadband Networks, and Advanced Internet Technologies.

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PREFACE:

Preface

This book is one in a series of books called, "Emerging Communications Technologies." As the name of the book implies, the focus is on the Point-to-Point Protocol, and the Layer 2 Tunneling Protocol (L2TP).

The subject matter of this book is vast and my approach is to provide a system view of the topic. In consonance with the intent of this series, this general survey also has considerable detail, but not to the level of detail needed to design a system. For that, I leave you to your project team and the various specifications that establish the standards.

This book is considered to be at an intermediate-to-advanced level. As such, it assumes the reader has a background in data communications and the internet protocol suite. Notwithstanding, for the new reader, I have provided several tutorials and guide you to them in the appropriate parts of the book.

I hope you find this book a valuable addition to your library.

CREDITS

I have relied on several Internet Request for Comments (RFCs) and Internet Drafts in certain chapters in this book. In some cases, I have summarized the RFCs with a short tutorial, and in other cases, I have extracted key points from the documents. I have so noted these instances in the appropriate part of the book.

Keep in mind that the Internet Drafts are works in progress, and should be viewed as such. You should not use the drafts with the expectation that they will not change. Notwithstanding, if used as general tutorials, the Drafts discussed in this book are "final enough" to warrant their explanations.

For all the internet standards and draft standards thefollowing applies:

Copyright The Internet Society (1998). All Rights Reserved.

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published, and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included in all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.

Table of Contents

Prefacexv
Chapter 1Introduction1
Why PPP was Developed1
What PPP Does2
Applications of PPP3
The Network Access Server (NAS)4
Operations of a Data Link Protocol5
Eliminating ACKs, NAKs, and Retransmissions7
The Data Link "Handshake"8
How PPP Fits into the Picture10
Beyond the Individual Link Operations: Layer Two Tunneling Protocol (L2TP)10
The Internet Layered Architecture10
Data Link Protocols and the Internet Model12
A General Look at PPP Operations13
The PPP Family15
Summary16
Chapter 2PPP, HDLC, and the Frames17
HDLC17
Relationship of PPP's Operations and HDLC19
Relationship of PPP to Network Control Protocols (NCPs)20
PPP and HDLC Formats20
Asynchronous HDLC (AHDLC)21
Octet-synchronous HDLC21
Bit-synchronous HDLC22
Explanation of Terms23
The PPP PDU24
Auto-Detect Operations25
PPP and Error Checking26
Error Checking and Retransmission26
Error Checking but no Retransmission28
Summary
Chapter 3The Principal PPP Entities: LCP29
Link Control Protocol (LCP) Basics29
The PPP Phases30
Link Dead (physical layer not ready)31
Link Establishment Phase31
Authentication Phase32
Network-Layer Protocol Phase32
Link Termination Phase32
Use of Timers During the Authentication and Network Layer Phases33
Introduction to the Options33
The PPP Option Negotiation Automaton33
Another Look at the Layered Architecture35
PPP States, Events, and Actions36
States37
Events38
Actions41
The LCP Information42
The LCP Packets43
Error Recovery46
Link Configuration Packets46
Link Termination Packets48
Link Maintenance Packets50
Summary52
Chapter 4The Principal PPP Entities: NCP53
Purpose of NCP53
Address Management and Assignment Operations54
The Internet Protocol Control Protocol (IPCP)57
Configuration Options58
The Internet Protocol Version 6 Control Protocol (IPv6CP)60
Other Network Protocols62
Open Systems Interconnection NCP (OSINLCP)62
System Network Architecture (SNA) NCP (SNACP)62
NetBIOS Frames NCP (NBFCP)63
Internetwork Packet Exchange NCP (IPXCP)63
Bridge NCP (BCP)64
Apple Talk NCP (ATCP)66
Xerox Network Systems Internet Datagram NCP (XNSCP)67
Banyan Vines NCP (BVCP)67
DECnet Phase IV NCP (DNCP)68
Summary68
Chapter 5PPP Security Operations69
What is Internet Security?69
Encryption Keys70
Private and Public Keys70
Distribution of Keys72
The Password Authentication Protocol (PAP)72
The Challenge-Handshake Authentication Protocol (Chap)74
The Chap Packets75
Radius78
Example of Radius Configuration78
The Radius Packet Exchange79
IPSec81
IPSec and the AH and ESP Operations83
IPSec and L2TP84
Other References84
Summary85
Chapter 6Other PPP Operations86
Recommended Extensions86
Vendor Extensions87
The OUI88
Maximum Receive Unit (MRU)88
Asynchronous Control Character Map (ACCM)88
Authentication Protocol90
Quality Protocol90
Magic Number90
Protocol Field Compression (PFC)91
Address and Control Field Compression91
PPP and LAPB92
The PPP Reliable Link Operations93
Running PPP Over X.2598
Running PPP Over ISDN98
Running PPP Over SONET99
Link Quality Monitoring (LQM)100
Other PPP Procedures101
FCS Alternatives101
Self Describing PAD101
Numbered Mode101
Multilink Procedure101
DCE Identifier102
Multilink Plus Procedure102
Link Discriminator102
Network-Layer Protocols102
Summary103
Chapter 7PPP Multilink Protocol (MP)104
Purpose of the Multilink Protocol (MP)104
Model for MP105
The PPP MP Approach106
MP Negotiation During LCP Operations107
Rules on the Use of PPP Options107
Configuration Options108
Packet Formats108
Example of MP Operations109
Example of Fragment-Loss Detection110
Guidance on Buffer-Space Requirements111
Protocol Extensions112
MP Configuration Option Types112
Multilink Maximum Received Reconstructed Unit (MRRU)113
Short Sequence Number Header Format Option113
Endpoint Descriminator Option114
PPP Bandwidth Allocation Protocol (BAP) and Bandwidth Allocation Control Protocol (BACP)114
BACP Operations115
BAP Operations115
Summary116
Chapter 8Layer Two Tunneling Protocol (L2TP)117
Purpose of L2TP117
Benefits of L2TP118
Terminology Dealing with L2TP118
How the Components Fit Together119
The L2TP Tunnel and Tunnel Sessions120
The L2TP Messages121
The L2TP Protocol Stack121
The L2TP Header and Messages (AVPs)122
The Fields Following the Header123
The AVPs123
AVP Categories124
The L2TP Control Messages128
Examples of L2TP Operations132
Window Management and Accounting for Traffic134
Slow Start134
Congestion Avoidance135
Security Considerations136
Tunnel Endpoint Security136
L2TP and IPSec136
Extensions137
Link Extensions137
Summary138
Chapter 9L2TP and Other Protocols and Services139
Running L2TP over ATM or Frame Relay139
Review of ATM and Frame Relay Excapsulation Procedures140
ATM and L2TP140
Frame Relay and L2TP143
L2TP-Over-IP MTU Path Discovery (L2TPMTU)144
Review of IP Fragmentation144
The Problem and Solution145
Problem with MTU Path Discovery on L2TP Tunnels145
L2TPMTU Operations146
Mobile PPP (MPPP)146
The Three Methods147
IPSec and L2TP150
The Compulsory Tunnel150
The Voluntary Tunnel151
Summary of L2TP Requirements for Security151
RADIUS and L2TP152
Other Type of Tunnels152
Authentication Alternatives152
Multiprotocol Label-Switching (MPLS) Extension155
Other Drafts of Interest156
Alternate Data Channel Extension156
L2TP Dynamic Data Window Adjustment156
IP Tunnel MIB157
Summary157
Appendix AHDLC Overview158
Appendix BThe Internet: Architecture164
Abbreviations205
Index209

Preface

PREFACE:

Preface

This book is one in a series of books called, "Emerging Communications Technologies." As the name of the book implies, the focus is on the Point-to-Point Protocol, and the Layer 2 Tunneling Protocol (L2TP).

The subject matter of this book is vast and my approach is to provide a system view of the topic. In consonance with the intent of this series, this general survey also has considerable detail, but not to the level of detail needed to design a system. For that, I leave you to your project team and the various specifications that establish the standards.

This book is considered to be at an intermediate-to-advanced level. As such, it assumes the reader has a background in data communications and the internet protocol suite. Notwithstanding, for the new reader, I have provided several tutorials and guide you to them in the appropriate parts of the book.

I hope you find this book a valuable addition to your library.

CREDITS

I have relied on several Internet Request for Comments (RFCs) and Internet Drafts in certain chapters in this book. In some cases, I have summarized the RFCs with a short tutorial, and in other cases, I have extracted key points from the documents. I have so noted these instances in the appropriate part of the book.

Keep in mind that the Internet Drafts are works in progress, and should be viewed as such. You should not use the drafts with the expectation that they will not change. Notwithstanding, if used as general tutorials, the Drafts discussed in this book are "final enough" to warrant their explanations.

For all the internet standards and draft standardsthefollowing applies:

Copyright The Internet Society (1998). All Rights Reserved.

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published, and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included in all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.

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